The invention relates to a prestressing element for the application of prestress to a measuring sensor between structures or within a recess of the structure.
Force sensors are placed under mechanical prestress for the use in many applications. Examples of such applications are measurements within mechanical structures, such as rollers or other machine elements to which a force is applied. On the one hand, such prestresses are required to keep the sensors in place and to exclude play. On the other hand, they shall ensure that the sensors are utilized in their linear measuring range even if temperature variations occur.
Prestressing elements for such purposes are already known. In EP 0433535 a measuring set-up is described having an adjustable wedge which brings the measuring element to a desired prestress by means of a screw. Two further screws which restore the wedge are used to loosen the prestress.
EP 0719405 also uses a wedge for prestressing the sensor. This wedge is integrated into the sensor. For this assembly, however, the presence of parallel surfaces is required. Also in this case, two further screws are used to release the prestress to restore the wedge.
In EP 0806643 the desired prestress is also generated by means of a screw extending through all sensors. The disadvantage of the device is that the screw extends in the direction of force flux which may lead to an error in the measurement.
What is interesting in the device, however, is the use of two sensors which are almost identical but arranged opposite to each other. A variation of the prestress caused by a temperature change generates the same variation on both sensors. Half of the difference of the values measured at each of these two sensors at each temperature corresponds to the desired value of the force acting at each sensor. A compensation of this type is important if the structure to be measured is subject to great temperature differences as for example in the case of rollers.
Another prestressing mechanism, for example the one described in DE 20119194 U1 requires a bore through the surface of the machine element, for example the roller. A destruction of the surface, however, is in many cases impossible or undesired.
Also in EP 1048370 a bore through the surface of a roller is required for the installation of the sensors.